As is commonly known, a glass capillary tube for holding an optical fiber (hereinafter, glass capillary tube), in which an insertion hole is formed into which the optical fiber is inserted and held, is used for holding the optical fiber in alignment with the optical axis of an optical component such as an optical waveguide-typed device. The glass capillary tube is fixed to an end surface of the optical component in a straight line in such a way that the central axis of the insertion hole and the optical axis of the optical component are precisely positioned. In this case, both the optical component and the glass capillary tube are usually provided on the same flat surface of a substrate (or casing or holder).
As specific examples, patent document 1 below discloses a glass capillary tube of which the exterior surface is substantially rectangular in shape (composed of four flat portions) and of which a central insertion hole, into which a single-core optical fiber is inserted and held, is formed, and an optical component connected to the glass capillary tube in a straight line. According to the patent document 1, the positioning of the optical axis of the optical fiber inserted into and held by the insertion hole and the optical axis of the optical component are determined by utilizing the flat portions on the exterior surface of the glass capillary tube.
Patent document 2 below discloses a glass capillary tube of which the exterior surface is composed of a single flat portion and a single partial cylindrical portion and in which an insertion hole for inserting and holding an optical fiber corresponding to the central axis of the partial cylindrical portion is fommed, and a rectangular optical waveguide device connected to the glass capillary tube in a straight line. According to the patent document 2, in the state where an auxiliary member is fixed to the upper surface of the connecting end of the optical waveguide device, the optical waveguide device and the glass capillary tube are connected and fixed.
Patent document 3 below discloses an optical waveguide device, of which the cross-section is approximately circular in shape, and a ferrule, of which the cross-section is approximately circular in shape for holding an optical fiber, provided such that the respective end surface of the two are connected and held in an inner opening of a single sleeve, and an insertion hole in the ferrule into which the optical fiber is inserted and held is formed in a position deviated (de-centered) from the center of the ferrule.
[Patent Document 1] Japanese Unexamined Publication No. 2001-318270
[Patent Document 2] Japanese Unexamined Publication No. 2003-287651
[Patent Document 3] Japanese Unexamined Publication No. H2-236508